Quantifying Nursery Habitat Function: Variation in Habitat Suitability Linked to Mortality and Growth for Juvenile Black Drum in a Hypersaline Estuary

Abstract

The Black Drum Pogonias cromis population in the Upper Laguna Madre (ULM), Texas, USA, is known to exhibit regionally unique population dynamics and life history strategies in comparison with other populations. I examined regional variation in nursery habitat suitability for Black Drum on the Texas coast and further identified functionality of habitat variables in the ULM as it is related to the unique population dynamics observed in this bay system. Rank and relative importance of habitat variables for Black Drum in other regions of the Texas coast were found to differ from those for the ULM population. Furthermore, directionality of salinity and inlet distance differed in the ULM, indicating that increased recruitment in this system was tied to salinities greater than 40‰ and areas at the greatest distance from Gulf of Mexico inlets (i.e., Baffin Bay). Peak mortality and growth rates were found to occur at approximately the same mean salinity value (33‰), with decreases in both as salinity increased. Temperature and dissolved oxygen also exhibited quantifiable relationships with vital rates, although the salinity relationships were most striking. The relationship between growth, mortality, and CPUE suggested that observed recruitment of Black Drum in the ULM is a complex interaction between suitable habitat (hydrographic variables) and density dependence. The identification of regional variation in habitat relationships and the quantification of habitat functionality are crucial steps in interpreting population dynamics and formally incorporating such metrics into stock assessment. This movement from concept to quantification is key to making habitat protection and restoration a true priority in the fisheries management realm.